Intent to unship: overflow/underflow events

[Gregory Pappas]

As of Firefox 131, I intend to disable the non-standard overflow/underflow events.

Summary

The overflow event fires when an element's content overflows; the underflow event fires when an element's content stops being overflowed.

Motivation
These events are problematic because they expose when layout happens. This makes standardizing them and achieving interoperable implementations practically impossible.

Alternatives
Authors can use ResizeObserver or IntersectionObserver for similar functionality.

Bug: bug 1907460
Specification: N/A
Standards body: N/A
Platform coverage: All  
Preferences: layout.overflow-underflow.content.enabled, layout.overflow-underflow.content.enabled_in_addons

Other browsers:

• WebKit: Has a similar overflowchanged event, there's some discussion in bug 67583 about removing it
• Blink: Inherited overflowchanged from WebKit, removed it in 2015 (issue 460822)